The reaction between elemental phosphorus p4(s) and o2(g) to make p4o10(s):

The reaction between elemental phosphorus p4(s) and o2(g) is a synthesis type of reaction where two elements combine together to form a compound. Balancing the equation, we get P4(s) + 5 O2(g) = P4O10(s). Here the number of oxygen molecules are balanced on either side by adding 5 molecules of O2 on the product side.